1. Field of the Invention
The present invention relates generally to semiconductor device packages. More particularly, it relates to semiconductor device packages having dummy block leads and/or tie bars having extending portions. Both the dummy block leads and the tie bar extending portions function to prevent the formation of air traps or voids in the encapsulate.
2. Background of the Related Art
Semiconductor device packages having a die pad onto which one or more chips is attached make up about 70-80% of the total semiconductor device package production. Such packages are advantageous in that they can be manufactured by simple methods using existing production equipment.
However, some problems may occur in their mass production. In particular, when their assemblies are encapsulated in a transfer mold with an encapsulate such as a potting resin, for example epoxy molding compound, turbulence is produced at or near the lead frame or electrical interconnection parts, resulting in the formation of air traps or voids in the resulting encapsulated package body. The air traps or voids at or near the lead frame or electrical interconnections cause package failures such as electrical shorts.
FIG. 1 is a partially cut away perspective view of a conventional semiconductor device package; FIG. 2 is a cross-sectional view taken along the line `2--2` in FIG. 1; and FIG. 3 is a cross-sectional view taken along the line `3--3` in FIG. 1.
With reference to FIGS. 1 through 3, the semiconductor device package 100 includes a chip 10, a die pad 30 and inner leads 50. The chip 10 is attached to an upper surface of the die pad 30 by way of an adhesive 20 such as Ag-epoxy adhesive. The chip 10 is electrically connected to the inner leads 50 by way of bonding wires 70. The die pad 30 is mechanically linked to side rails (not shown) via tie bars 40.
The package 100 also has an encapsulate covering the chip 10, die pad 30, tie bars 40, inner leads 50, and electrical interconnections including bonding wires 70 to form a package body 80. The encapsulate may be potting resins such as epoxy molding compounds.
Outer leads 60, which are formed integrally with inner leads 50, extend from the package body 80, and are formed, for example, in a J-shape suitable for mounting onto external devices.
FIG. 4 depicts the flow of the potting resin within the mold during the encapsulation of the package assembly. In cavities 312, 412 defined by the upper mold die 310 and the lower mold die 410, the package assembly is encapsulated with the potting resin introduced through a gate 414 of the lower mold die 410.
The arrows in the drawings indicate the flow of the potting resin within the cavity. As the potting resin collides with the chip 10 and the die pad 30, its velocity drops, while the potting resin near the inner wall of the mold dies 310, 410 retains its original velocity. This results in a deviation of the flow velocity of the potting resin within the cavities 312, 412. The deviation generates turbulence in the potting resin flow, and consequently, the formation of air traps or voids in the resulting package body 80. This is even more significant when the package assembly contains a larger chip.
When the package is subjected to reliability tests which are performed under an elevated temperature and an elevated pressure, water vapor is supplied into the package body. If the package has air traps or voids therein, the water vapor localizes at the air traps or voids and then expands. This may adversely affect the mechanical strength of the package body 80 and deteriorate the package reliability.
Moreover, for packages having a multi-pin lead frame, the potting resin collides with the inner leads (50 in FIG. 1) and generates turbulence as well. This causes the formation of air traps near or at inner leads 50, resulting in electrical shorts of bonding wires 70 electrically connecting the inner leads with the chip.